I get these all the time too! My uncle has had them his whole life and has tried so many 'cures but nothing has worked.
There a whole bunch of explanations as to why you can get them. Too much tea, coffee, late nights, spicy food, unhealthy living, not bushing your teeth regularly, stress....the list goes on and on.
I went to the dentist last December to get a tooth removed and it was a very difficult extraction, took over an hour to remove as she drilled and picked at it. Anyway, I ended up getting 8 ulcers at once! The dentist told me it was probably the stress that my mouth went under that made it break out. The worst thing was that it was a week before Christmas......not the most pleasant Christmas dinner I've ate.
I'm I ever going to get to the point....... I think what you should do is try and think of something that you have all the time and try cutting it out, it may be that one thing that's causing them. Other than that just make sure you have instead gel handy because if you feel one coming on it will go away much quicker if you treat it straight away.
Good luck,
Dave